Reuse: composite actions and reusable workflows

Goal

Know the two ways to stop copying YAML, and when to use each.

Composite actions share steps

Every backend job needs Node.js, the cache and npm ci. Those steps live once in .github/actions/setup-backend/action.yml:

name: Set up the backend
inputs:
  node-version:
    required: false
    default: '22'
runs:
  using: composite
  steps:
    - uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
      with:
        node-version: ${{ inputs.node-version }}
        cache: npm
        cache-dependency-path: backend/package-lock.json
    - name: Install dependencies
      run: npm ci
      shell: bash
      working-directory: backend

Any job uses it as a step, after checking out the code (the action lives in the repository):

- uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
- uses: ./.github/actions/setup-backend
  with:
    node-version: '24'

Note shell: bash on run steps: composite actions must say which shell to use.

Reusable workflows share whole jobs

.github/workflows/reusable-test.yml is a complete test job that takes an input:

on:
  workflow_call:
    inputs:
      node-version:
        type: string
        required: true

nightly.yml calls it as a job, not a step:

jobs:
  test:
    uses: ./.github/workflows/reusable-test.yml
    with:
      node-version: ${{ inputs.node-version || 'node' }}

Which one?

Both can live in another repository too, for sharing across a team.

Check it works

Change the default node-version in the composite action to '24' on a branch and open a pull request: the Build job now runs on Node 24, because it does not pass a version.

Exercise

Make ci.yml's Build job pass node-version: '22' explicitly, so it no longer depends on the action's default.